1. Field of the Invention
The invention relates to an optical sensor arrangement having a light emitting arrangement for the feeding-in of a first emission light beam into a first emission optical waveguide and a second emission light beam into a second emission optical waveguide, having a polarizer, coupled with the two emission optical waveguides for the generation of a linearly polarized light beam from both the first and second emission light beam, and having an optical sensor for the alteration of the state of polarization of a supplied polarized light beam as a function of a physical quantity acting on the sensor and for the supply of a sensor light beam formed from a polarized light beam.
2. Description of the Related Art
An optical sensor arrangement of the type referred to above is known from FIG. 2 of EP-A-0,175,358. In this case, a first light source conducts a first emission light beam via a first coupler and a microlens into a first optical waveguide. At the other end of the optical waveguide, the emission light beam is irradiated via a second microlens into a polarization splitter. The polarization splitter generates from the emission light beam a linearly polarized light beam which is passed to an optical sensor. The polarized light beam alters its state of polarization as a function of a physical quantity acting on the sensor, e.g. by pressure or an electrical or magnetic field. Via a retardation plate with a retardation of 1/8th of a wavelength, the light beam emitted by the sensor is radiated onto a mirror, which reflects this light beam. Via the retardation plate and the optical sensor, the reflected light beam is radiated onto the polarization splitter, which generates two linearly polarized light beams. The first linearly polarized light beam is passed via the first optical waveguide to the first coupler, which deflects the light beam and conducts it into a first photodetector. The second linearly polarized light beam is irradiated via a microlens into a second optical waveguide and passed via a further microlens to a second coupler, which radiates the light beam into a second photodetector.
In the known arrangement, a second emission light beam, which temporally follows the first emission light beam, is irradiated from a second light source into the second optical waveguide. After the light beam generated by the second light source has passed through the polarization splitter, the optical sensor and the delay plate, the light beam incident on the mirror is reflected. After the reflection, the polarization splitter splits up the reflected light beam into two linearly polarized light beams and irradiates a respective linearly polarized light beam into each one of the two optical waveguides. After passing through the couplers, the linearly polarized light beams are received by respective photodetectors. From the total of four light intensities--converted into electrical signals--of the light beams received by the two photodetectors, a measure for the physical quantity is computed in a computing circuit, which measure is independent of the attenuation of the optical waveguides.
In this known optical sensor arrangement, reflections occur at optical boundary surfaces (e.g. the boundary surfaces at the polarization dividers, the microlenses, the sensor element and possibly at the plug-in connections for the optical waveguides), which are superposed upon the light beams at the photodetectors (light receiving arrangement). On account of these reflections, the measurement result is falsified. Moreover, in addition, in order to separate reflected and transmitted light beams couplers must be used, in which an additional light loss occurs as a result of attenuation in the coupler and as a result of the light splitting of the coupler.
FIG. 3 of EP-A 0,175,358 furthermore discloses an optical sensor arrangement in which a semi-transparent mirror is used. In this case, there is connected at one end of a first optical waveguide a coupler which receives a light beam from a first light source and sends a light beam to a first photodetector. Between the other end of the first optical waveguide and the semi-transparent mirror there is disposed a polarization splitter, which generates a linearly polarized light beam, an optical sensor and a retardation plate. The mirror reflects a part of the light beam and transmits the other part. On the other side of the mirror there is connected a second optical waveguide, which leads to a second coupler with light source and photodetector. As in the arrangement according to FIG. 2, light beams are emitted with a time shift via the two optical waveguides. In this case also, reflections take place at optical boundary surfaces.